Re: [PATCH v10 6/7] x86/arch_prctl: Add ARCH_[GET|SET]_CPUID

[Kyle Huey]

On Wed, Nov 9, 2016 at 5:21 AM, Borislav Petkov <bp@xxxxxxx> wrote:
> On Tue, Nov 08, 2016 at 09:06:31PM +0100, Thomas Gleixner wrote:
>> The upcoming ring3 mwait stuff can add its magic to tweak that MSR into
>> this function.
>>
>> Stick the call at the end of init_scattered_cpuid_features() for now. I
>> still need to figure out a proper place for it.
>
> So Thomas and I discussed this more on IRC and I think we can get rid
> of the MSR iterating in scattered.c and integrate both the R3 MWAIT and
> CPUID faulting like this:
>
> ---
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index fcd484d2bb03..5c38a85af2e7 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -452,6 +457,39 @@ static void intel_bsp_resume(struct cpuinfo_x86 *c)
>         init_intel_energy_perf(c);
>  }
>
> +static void init_misc_enables(struct cpuinfo_x86 *c)
> +{
> +       u64 val, misc_en;
> +
> +       if (rdmsrl_safe(MSR_MISC_FEATURES_ENABLES, &misc_en))
> +               return;
> +
> +       misc_en &= ~MSR_MISC_ENABLES_CPUID_FAULT_ENABLE;
> +
> +       if (!rdmsrl_safe(MSR_PLATFORM_INFO, &val)) {
> +               if (val & PLATINFO_CPUID_FAULT_BIT)
> +                       set_cpu_cap(c, X86_FEATURE_CPUID_FAULT);
> +       }
> +
> +       wrmsrl(MSR_MISC_FEATURES_ENABLES, misc_en);
> +       this_cpu_write(msr_misc_features_enables_shadow, misc_en);
> +}
> +
>  static void init_intel(struct cpuinfo_x86 *c)
>  {
>         unsigned int l2 = 0;
> @@ -565,6 +603,8 @@ static void init_intel(struct cpuinfo_x86 *c)
>                 detect_vmx_virtcap(c);
>
>         init_intel_energy_perf(c);
> +
> +       init_misc_enables(c);
>  }
>
>  #ifdef CONFIG_X86_32
> ---
>
> Please redo your patchset and add the detection to init_intel() like above.
>
> Also, let's call that MSR mask MSR_MISC_ENABLES_CPUID_FAULT_ENABLE like
> the rest of the bits in msr-index.h

There's already an IA32_MISC_ENABLE, so I've made this
MSR_MISC_FEATURES_ENABLES_CPUID_FAULT instead.

- Kyle